Answers

Going through your question and detail I could see you are having this same issue now which I faced few years ago with my WordPress setup.

For information all shared hosting provider use default linux SMTP to send outgoing emails which use sendmail to deliver emails and most of the time they miss-out important sending domain configuration like SPF, DKIM, DMARC records. And impact email delivery.

Don't worry about this as these can be easily fixed with following setup.

In order to fix this, you should use SMTP relay like ( ESP ) to deliver email externally, but here you should configure following important records on your email sending domain name:
SPF record according to your SMTP relay provider
DKIM record according to your SMTP relay provider
DMARC according to your sending domain name

Apart from above also configure your email sending domain name to your Google Postmasters account ( This is like Google webmasters for emails ).

This technology setup improved my email to all subscribers and my email open rate boosted from mere 17% to 48%.

Coming to SMTP email service provider, looking at your requirement, I would recommend to use SendGrid or SparkPost. SparkPost is quite easy to configure.

I hope you are specifically interested in Partner Marketing practices which is being said according to your question.
But later looking at the detail you are diving deep into affiliate kind of model where you want to work with Promotional Partners.
Let me tell you both Referral Marketing and Affiliate Marketing are different models to work with, which falls under Partner marketing. Here are few differences:
In affiliate marketing the advocate doesnot know their referred customers personally, and the primary reason for referring your brand is financial motivation.
Whereas, Referral marketing advocates recommend your brand to direct friends or family members and motivation is based on a strong relationship between the advocate and the potential customer.

Both of the above practices under Partner marketing have different approach to hire the partners and work with them. It also depend on your stage of company at which they want to deploy which practice / strategy.

Further you can use these tools:
Hasoffers, Cake, Getambassador, OSI Affiliate Software, Offerslook to create individual Partner Marketing Site for your product / service promotion. Go for their whitelabel solution and using them you would be able to create Partner Marketing Site.

It all depend on what goal you want to achieve. For both growth and sales there are different affiliates who can help you. Before you start with affiliate you should know following things first:
> Ideal customer persona of your product or service
> You have infrastructure ready for growth
> You have a dedicated resource to handle affiliates and their queries
> You have proper finance and accounts setup available.
> Your current churn rate of your service are incredibility low.

Having above things in place you can go ahead recruiting right fit of affiliate partner for your product or service. Yes, having good affiliate partner onboard help you increase growth of your product / website / service.

You can get in touch through direct email or tweet with a catchy pitch.
To find personal email address you will have do little bit of research.
Also you should target only niche journalists who can understand and write about startup. To do this, search your product business category on Google News and get touch with journalists who recently wrote on that particular topic of yours.